Controlling method of seat belt retractor

ABSTRACT

In controlling a seat belt retractor, at least one of signals selected from a state signal showing a movement of an occupant wearing a seat belt and an external signal obtained from detecting means installed in a vehicle during running thereof is received. Then, a rotation of a spool for a webbing is controlled by switching a rotational torque of a motor to a predetermined reduction ratio corresponding to at least one of the state signal and the external signal, or a driving state of the motor is controlled to a predetermined torque, to thereby wind the webbing on the spool. After fastening the seat belt, the seat belt is automatically wound, and after a predetermined time from completion of winding of the webbing, it is determined whether the winding of the webbing is further needed, and if necessary, the webbing is wound again.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 09/484,450 filed on Jan.18, 2000, now patented as U.S. Pat. No. 6,427,935 issued on Aug. 6,2001.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a controlling method of a seat beltretractor, i.e. motorized seat belt retractor, which can change itsoperating condition to correspond to the state of an occupant wearing aseat belt or to external signals.

In a seat belt retractor provided in an automobile, it is preferable toretract an excess amount of a seat belt after the seat belt is pulledand a tongue is engaged with a buckle device, without applying too muchstress to the chest or other portions of an occupant normally wearingthe seat belt.

Normally used for winding up a seat belt in a seat belt retractor is abiasing force of a single return spring. When a spring providing a smallbiasing force is employed in order to reduce stress applied to the chestof an occupant, the force for winding or retracting the seat beltbecomes weak, thus lowering its operation and its accommodation to theretracted state.

To the contrary, when a spring for providing a large biasing force isemployed in order to provide an enough winding force for its retraction,the stress to be applied to the chest of the occupant normally wearingthe seat belt is increased.

Since a single return spring is employed, a conventional seat beltretractor has a problem that the biasing force of the return springincreases as the amount of withdrawal of the webbing (hereinafter, theterm “webbing” is used for referring to the belt itself in thisspecification) is increased because the return spring is repeatedlywound.

As one of means for solving the problem with regard to the winding of awebbing caused by using a single return spring, the applicant hasdeveloped a tension reducing mechanism for reducing the retractionforce, which comprises two rope pulleys of truncated cone shape with ahelical guide groove (see Japanese Patent No. 2711428).

On the other hand, the applicant also has developed a seat beltretractor in which a tension control for a seat belt is performed by abuilt-in electric motor to improve comfortableness as one of functionswhen an occupant normally wears, and to correspond to a distance fromanother vehicle running in front of or behind its own vehicle (seeJapanese Unexamined Patent Publication No. H09-132113).

In the seat belt retractor disclosed in the aforementioned publicationNo. H09-132113, an ultrasonic motor is employed as a driving unit forthe tension control and a spring mechanism is provided as a main windingmechanism. The motor is employed for controlling the tension on the seatbelt when the occupant wears the seat belt, and for controlling thewinding and unwinding of the seat belt to correspond to external signalsinputted during running of the vehicle. Therefore, it is required torotate the motor in reverse. This makes the control circuit complex.Since the operation of winding up the seat belt is performed by twocircuits, there is also a problem that it is hard to smoothly switch theoperation of winding up the seat belt according to the inputted externalsignals.

When the external signals from sensors mounted on the vehicle are set tofunction as the trigger of the motor, a speed-reduction gear to bedriven by the motor employed in the seat belt retractor can not copewith a wide range of a winding mode because the reduction range allowedby the speed-reduction gear is limited.

Therefore, it is an object of the present invention to solve theproblems of the prior art and to provide a seat belt retractor in whicha seat belt can be wound by only a motor with a simple control circuitand a driving mechanism, and the winding mode can be set widely tocorrespond to external signals inputted when an occupant wears the seatbelt and a vehicle runs, and to provide a control method for the seatbelt retractor.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

To solve the aforementioned problems, the present invention provides aseat belt retractor comprising: a base frame; a spool journalled at aspool shaft to the base frame; a speed-reduction mechanism; and a motorfor rotating the spool via the speed-reduction mechanism for winding upa webbing onto the outer periphery of the spool. The speed-reductionmechanism has two transmission trains with different reduction gearratios, switching means for switching the transmission trains to one ofthe trains corresponding to a driving signal obtained from externalunits, and resistant torque means having a preset value so that atransmission element common to the two trains transmits rotation of themotor when the torque of the rotation is smaller than the preset value.

The driving signal is preferably set according to a state signalobtained by movement of an occupant wearing the seat belt and anexternal signal obtained from detecting means installed in a vehicleduring the running of the vehicle.

It is preferable that when the state signal is received, the rotationaltorque is reduced at a small reduction gear ratio to be smaller than thepreset value of the resistant torque means, and the spool shaft isrotated with the reduced rotational torque for winding up the webbing.

It is preferable that when the external signal is received, theswitching means switches the transmission trains so that the rotationaltorque is increased at a large reduction gear ratio to exceed the presetvalue of the resistant torque means to wind the webbing.

It is preferable in the above that the resistant torque means is a slipmechanism comprising a viscosity resistant element disposed on thetrains of the speed-reduction mechanism.

It is also preferable that the switching between the trains is achievedby actuating the switching means according to the driving signal whenthe external signal is received and securing a part of the transmissionelement disposed in the speed-reduction mechanism.

It is preferable that the switching means comprises a pawl mechanismwhich engages one of ratchet teeth formed on the outer periphery of aninternal gear in a planetary gear unit to stop the rotation of theinternal gear.

It is also preferable that the switching means comprises a pawlmechanism having two pawls journalled by shafts, which cooperate toengage ratchet teeth of the internal gear to stop rotation of theinternal gear.

In this case, it is preferable that the two pawls are a first pawl and asecond pawl, and the first pawl pivots about the shaft by excitation ofa solenoid to engage one of the ratchet teeth and, after that, the firstpawl makes the second pawl to engage another of the ratchet teeth.

It is preferable that a spring connected to the first pawl biases thefirst pawl after cancelling the excitation of the solenoid with theresult that the second pawl disengages from the ratchet teeth.

It is preferable that the rotation of the spool is reduced through areduction gear train, and the spool shaft is provided with a spoolrotation detecting unit for detecting a rotational direction and astopping state of the spool.

It is preferable that the withdrawal of the webbing is detected by thestart of rotation of the spool and acts as a trigger for turning ON apower source of a control circuit for driving the motor.

The present invention also provides, as another invention, a seat beltretractor comprising a base frame, a spool journalled at a spool shaftto the base frame, around which a webbing is wound, a return spring forwinding up the webbing by its return force, and a motor with aspeed-reduction mechanism for switching the winding of the webbing,wherein the speed-reduction mechanism has a transmission train with apredetermined reduction gear ratio and switching means for connectingthe transmission train to the spool shaft corresponding to a drivingsignal obtained from an external unit.

The driving signal is preferably set according to a state signalobtained by movement of an occupant wearing the seat belt and/or anexternal signal obtained from detecting means installed in the vehicleduring running of the vehicle.

It is preferable that when the external signal is received, theswitching means switches the transmission trains so that the webbing iswound by the return spring at a large reduction ratio.

It is preferable that the switching of the transmission train isachieved by actuating the switching means according to the drivingsignal when the external signal is received, and securing a part oftransmission elements disposed in the speed-reduction mechanism.

It is preferable that the switching means comprises a pawl mechanismwhich engages one of ratchet teeth formed on an outer periphery of aninternal gear in a planetary gear unit to stop the rotation of theinternal gear.

The present invention also provides, as a further invention, a seat beltretractor comprising: a base frame; a spool journalled at a spool shaftto the base frame around which a webbing is wound: a return spring forwinding up the webbing by its return force: and a motor with aspeed-reduction mechanism for winding up the webbing at a low speed forfitting the webbing to an occupant, wherein the speed-reductionmechanism has a contrate gear with a predetermined reduction gear ratioand wherein the webbing is wound by driving the motor via the contrategear.

The present invention also provides, as an invention for efficientlyoperating the above retractor, a control method of a seat belt retractorcomprising: receiving an external signal outputted to correspond to astate signal according to the movement of an occupant wearing a seatbelt and/or an external signal from detecting means installed in avehicle during running of the vehicle; switching transmission of arotational torque of a motor to a predetermined reduction ratiocorresponding to the state signal or the external signal, or controllingthe driving state of a motor to change its torque to a predeterminedvalue to control the rotation of a spool; and winding the webbing ontothe spool.

It is preferable that based on a state signal obtained by detectingwithdrawal of the webbing while the webbing is in the wound state, therotation of the motor is stopped.

It is preferable that based on a state signal obtained by detecting thata tongue is engaged with a buckle, the motor is driven with such torqueas to wind the webbing to fit the webbing to the occupant's body.

It is preferable that based on a state signal obtained by detecting thatthe fitting of the webbing is accomplished, the torque of the motor isreduced or the drive of the motor is stopped.

It is preferable that based on a state signal obtained by detecting thatthe withdrawal of the webbing is cancelled, the motor is restarted towind the webbing.

It is preferable that when the withdrawal of the webbing is made andstopped while a tongue is engaged with a buckle, the winding of thewebbing is started to fit the webbing to the occupant and, after that,the torque of the motor is reduced or the drive of the motor is stopped.

It is preferable that the torque of the motor for fitting the webbing tothe occupant is set lower than the torque of the motor for fitting thewebbing to the occupant just after the tongue is engaged with thebuckle.

It is preferable that based on a state signal obtained by detecting thata tongue is disengaged from a buckle, the motor is activated to wind thewebbing into the retractor.

It is preferable that at the same time of or after a predeterminedperiod of time from the detection of the withdrawal of the webbing, apower source of a control circuit for operating the motor is turned ON.

It is preferable that at the same time of detection that the winding ofthe webbing is accomplished, or detection that the webbing has not beenwithdrawn for a predetermined period of time, a power source of thecontrol circuit for operating the motor is turned OFF.

It is preferable that the control method further comprises: switchingthe torque of the motor to a preset value or a variable value byswitching means according to an obtained external signal to wind thewebbing by the motor.

It is preferable that the control method further comprises: providing amode in which the switching means is not returned so as to hold thedriving state of the motor after being switched.

It is preferable that the control method further comprises: providing amode in which the switching means is not returned so as to hold thedriving state of the motor after being switched through torque resistormeans of the speed-reduction mechanism.

It is preferable that the mode is a holding mode during running of thevehicle or a child seat fixing mode.

It is also preferable that the control method further comprises:transmitting a command signal of the motor corresponding to the externalsignal as information to be used for one or all of the seat beltretractors installed in vehicle seats in a communicating method capableof recognizing the seats so as to perform the mode setting for thevehicle seats.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing components of a seat beltretractor according to an embodiment of the present invention;

FIG. 2 is an exploded perspective view showing components of aspeed-reduction mechanism of the seat belt retractor of the presentinvention;

FIG. 3 is a cross-sectional view showing end faces of transmissionelements inside the speed-reduction mechanism;

FIG. 4 is a cross-sectional view showing sections of transmissionelements inside the speed-reduction mechanism;

FIG. 5 is an exploded perspective view showing a variation of aretracting mechanism of the seat belt retractor;

FIG. 6 is an exploded perspective view showing another variation of aretracting mechanism of the seat belt retractor;

FIG. 7 is an explanatory view schematically showing components forcontrolling mechanisms and units composing the seat belt retractoraccording to the present invention;

FIG. 8 is an end view showing the structure of a webbing withdrawaldetecting unit and a spool rotation detecting unit;

FIGS. 9(a)-9(c) are explanatory views schematically showing thestructure and the operation of a first example of a pawl mechanism;

FIG. 10 is partially exploded perspective view showing a secondembodiment of a structure of a pawl mechanism;

FIGS. 11(a)-11(d) are explanatory views schematically showing thestructure and operation of the pawl mechanism shown in FIG. 10;

FIGS. 12(a)-12(c) are explanatory views schematically showing variationsof a switching mechanism of the speed-reduction mechanism;

FIGS. 13(a) and 13(b) are explanatory views showing the linkage betweena reduction gear mechanism and a slip mechanism;

FIGS. 14(a) and 14(b) are explanatory views showing the switchingoperation in a planetary gear unit;

FIG. 15 is an explanatory view showing a state of withdrawal of awebbing while the webbing is wound;

FIG. 16 is a flow chart showing the operational flow for controlling thewinding of the webbing;

FIG. 17 is a flow chart showing the operational flow for setting eachmode;

FIG. 18 is a flow chart showing the operational flow for preventinglooseness of the webbing while an occupant wears the seat belt;

FIG. 19 is a variation diagram showing a relation among a signalcurrent, unwound amount of the webbing, and tension for winding up thewebbing in each mode of winding the webbing;

FIG. 20 is a variation diagram showing the controlling state of themotor speed corresponding to the withdrawal or retraction of thewebbing;

FIGS. 21(a)-21(e) are explanatory views schematically showing variationsof the entire structure of the speed-reduction mechanism;

FIGS. 22(a)-22(c) are explanatory views schematically showing variationsof a first reduction gear mechanism;

FIGS. 23(a)-23(c) are explanatory views schematically showing variationsof a second reduction gear mechanism;

FIGS. 24(a) and 24(b) are explanatory views schematically showingvariations of a switching mechanism of the speed-reduction mechanism;

FIGS. 25(a)-25(d) are explanatory views schematically showing variationsof a slip mechanism;

FIGS. 26(a)-26(d) are explanatory views schematically showing variationsof the slip mechanism; and

FIGS. 27(a) and 27(b) are explanatory views schematically showingvariations of a webbing withdrawal detecting unit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the seat belt retractor and the controlmethod for carrying out the present invention will be described withreference to the accompanying drawings.

FIG. 1 is an exploded perspective view illustrating a schematicstructure of an assembly of the seat belt retractor 1 of the presentinvention including a webbing winding reel 2A; a reel locking mechanism4; a speed-reduction mechanism casing 11 for accommodating a motor 5 asa driving mechanism and a speed-reduction gear mechanism; a planetarygear unit 30 composing a part of the speed-reduction gear 10 (FIG. 2);and detecting units 40 and 50 for controlling the motor. FIG. 2 is anexploded perspective view showing an internal structure of thespeed-reduction mechanism 10 among the components shown in FIG. 1.

In FIG. 1, the webbing winding reel 2A and the reel locking mechanism 4as the known mechanisms are illustrated in the assembled state. Thewebbing winding reel 2A comprises a spool 2 on which a webbing W iswound and a base frame 3 rotatably supporting a spool shaft 15 of thespool 2, and the reel locking mechanism 4 (only its outer profile isshown) for preventing the rotation of the spool 2 is integrally attachedto the base frame 3. In this embodiment, a single variable speed DCmotor 5 is employed as its driving mechanism. A control unit 9 (see FIG.7) is provided with a circuit device (not shown) in order to control therotational speed of the DC motor 5. As a driving mechanism to which arotational torque is transmitted from the DC motor 5, thespeed-reduction mechanism 10 is arranged in the speed-reductionmechanism casing 11.

The speed-reduction mechanism 10 includes a first reduction gearmechanism or train 10A and a second reduction gear mechanism or train10B so as to have two trains. The operation of rotating the spool 2 isachieved through one train by one of the speed-reduction gearmechanisms. At this point, to prevent rotational torque transmitted fromone driving machine, such as motor, from being transmitted directly tothe two trains, a slip mechanism (hereinafter, designated by numeral 60)as resistant torque means 60 is arranged between gears to slip rotationby a predetermined resistant torque to shut off the transmission of therotational torque through one of the trains. The arrangement of the slipmechanism 60 allows the speed-reduction gear to be switched to havedifferent reduction by switching means 70.

As shown in FIG. 1, the base frame 3 is a steel product having achannel-like configuration and includes right and left side walls 3 a(not shown) which are provided with supporting holes 3 b (not shown)into which end flanges of the spool 2 are loosely fitted. Formed on aninner periphery 3 c of one of the supporting holes 3 b are teeth (notshown) to which a pawl (not shown) is moved by the locking operation ofthe reel locking mechanism 4 well known so as to engage one of them.This engagement prevents the rotation of the spool 2 when the webbing Wis rapidly withdrawn from the retractor 1 so as to prevent the withdrawnof the webbing. Fixed to the other side wall 3 a of the base frame 3 isthe speed-reduction mechanism casing 11 for housing the assembly of thespeed-reduction mechanism 10 for increasing the rotational torque of themotor 5. The speed-reduction mechanism casing 11 is fixed to the sidewall 3 a through the planetary gear unit 30.

Attached to the outer end of the speed-reduction mechanism casing 11 andthe outer end of the reel locking mechanism 4 are a webbing withdrawaldetecting unit 40 and a spool rotation detecting unit 50, respectively.A motor gear 6 is arranged in a lower portion of the speed-reductionmechanism casing 11 so as to transmit a predetermined rotational torqueto the assembly of the speed-reduction mechanism 10 (its structure willbe described later). It should be noted that a casing for housing themotor 5 is not illustrated for simplifying the drawing.

The structure of the speed-reduction mechanism will be described withreference to FIG. 2 through FIG. 4.

As described above, the speed-reduction mechanism 10 comprises the firstreduction gear mechanism 10A and the second reduction gear mechanism 10Bto compose two trains, which commonly utilize parts of the transmissionelements. In this embodiment, a pawl mechanism driven by an electricsolenoid 71 is employed as the switching means 70 for switching theoperation of the reduction gear mechanisms.

The components of the first reduction gear mechanism 10A will bedescribed with reference to FIG. 2 through FIG. 4. FIG. 3 is a sectionalview showing the inside of the seat belt retractor 1 illustrating endfaces of the components (gear) in detail for explaining the engagedstate of the transmission elements of the speed-reduction mechanism 10,and FIG. 4 is a sectional view showing the inside of the seat beltretractor 1 illustrating sections of the components (gears) in detailfor explaining the supporting state of the transmission elements of thereduction gear mechanism 10.

As shown in FIG. 1 and FIG. 3, the motor 5 is securely fixed to a lowerend of the base flame after the motor gear 6 is inserted through a lowerhole 11 a formed in the speed-reduction mechanism casing 11. The motorgear 6 is engaged with a double gear 12 supported by a rotational shaft(not shown) inside the casing 11. Though the double gear 12 is composedof two separate gears in FIG. 2, the double gear 12 may be formedintegrally. A small gear 12 a of the double gear 12 is engaged with areduction gear 13. The reduction gear 13 has a shaft boss 14, which isfitted over a hexagonal bush 16 coaxially integrally formed on a sungear 31 (the planetary gear unit 30 will be explained later). The sungear 31 is loosely fitted over a projection 15 a of the spool shaft 15so that the reduction gear 13 is journalled by the projection 15 a.Formed in the entire side outer surface of the reduction gear 13 is aflat recess 13 a. A rotary damper 17 well known in the art is fixed to aside surface of the recess 13 a. A gear 19 is journalled by a rotorshaft 18 of the rotary damper 17. Oil is sealed within the rotary damper17. A constant resistant torque is applied to the rotor shaft 18 by astructure that a rotor vane (not shown) turns in the oil to developviscosity resistance. Further, housed in the recess 13 a is a spooldriving gear 20, which is fixed to a hexagonal spline 15 b formed at theend of the projection 15 a. The rotation of the spool driving gear 20provides a predetermined rotational torque to the shaft end of the spoolshaft 15.

The structure of the planetary gear unit 30 arranged coaxially with thespool shaft 15 will now be described with reference to FIGS. 1, 3 and 4.

As clearly shown in the exploded perspective view of FIG. 1, theplanetary gear unit 30 comprises two planetary gears 32 which engage thesun gear 31 rotating at the same speed as the reduction gear 13, acarrier 33 which journals the planetary gears 32 and is rotatablecoaxially with the sun gear 31, and an internal gear 34 having internalteeth 37 with which the planetary gears 32 contact and engage. Amongthese components, the carrier 33 has a hexagonal socket 35 on the backsurface thereof. The socket 35 is fitted over a hexagonal large-diameterportion 15 c when the spool shaft 15 is inserted for assembly. Formed onthe entire outer periphery of the internal gear 34 are ratchet teeth 36.The pawl mechanism 70 is engaged with one of the ratchet teeth 36, whichwill be described later. The engagement between the ratchet teeth 36 andthe pawl mechanism 70 fixes the internal teeth 34, so that the rotationinputted from the sun gear 31 is transmitted to the carrier 33 with therevolution of the planetary gears 32 so as to rotate the large-diameterportion 15 c of the spool shaft 15 via the socket 35 at a large speedreducing ratio.

With reference to FIG. 5, description will now be made as regard to avariation in which a conventional spiral spring as a return spring isincorporated in a retractor. In this variation, comparing with thestructure shown in FIG. 2, the return force of the return spring isutilized for rotating the spool shaft in the webbing winding directionin a normal operation. Formed on the end of the projection 15 a of thespool shaft 15 is a cotter 15 d on which a spring bush 101 is fitted. Aninner end 102 a of the return spring 102 as the spiral spring is fixedto the spring bush 101, whereby a torque developed by the winding orunwinding of the return spring 102 is transmitted to the spool shaft 15.A spring cover 103 is fixed to the casing 11 by bolts (not shown) tocover the entire return spring 102. In the seat belt retractorstructured as mentioned above, the webbing is wound up by the returnspring 102 in a normal operation, while the webbing can be wound up bythe motor 5 additionally when the retraction of the seat belt isrequired in running of the vehicle.

FIG. 6 is a partial perspective view showing parts of the structure of avariation of the speed-reduction mechanism, in which the aforementionedfunction for the large reduction gear ratio is omitted to improve thecomfortableness for the occupant wearing the seat belt. As shown in FIG.6, the projection 15 a of the spool shaft 15 extends through a boss 110a of a contrate gear 110 for a large reducing ratio housed in the casing11 and fixed to the inner end of the return spring (see FIG. 5). Thecontrate gear 110 is a large gear on which cone-shaped teeth are formedat a constant pitch. On the other hand, an electric motor 112 is housedin the casing 11 in such a manner that the rotational shaft of the motor112 and the spool shaft 15 cooperate to form a skew gear to have a rightangle or a predetermined inclination angle. The electric motor 112 isprovided at its shaft end with a driving gear 114, which engages thecontrate gear 110. The rotation of the electric motor 112 is transmittedto the contrate gear 110 with reducing its speed so as to achieve thelow speed rotation of the spool shaft 15. The electric motor 112 isactivated when the occupant wears the seat belt, whereby the excessamount of the webbing (not shown) is withdrawn to such an extent not toprovide overpressure to the chest of the occupant so that the webbinglightly fits the body of occupant. The winding of the webbing isperformed by the aforementioned return spring while the vehicle isrunning. Thus, the omission of the function for the large reduction gearratio enables to manufacture a compact retractor at a low cost.

FIG. 7 shows a schematic structure of the seat belt retractor mentionedabove including the respective mechanisms, the control unit foroperating these mechanisms to link with each other, and the respectivedetecting units and detecting sensors for sending operational signalsrequired by the control unit.

Schematically shown in FIG. 7 are the retractor 1 mentioned above, thecontrol unit 9 disposed separately from the retractor 1 for performing apredetermined command operation to the respective mechanisms housed inthe retractor 1 as shown in FIG. 1 through FIG. 4, and external signalsensors for informing the state of the occupant wearing the seat beltand the state of the vehicle with regard to the safety.

That is, the spool 2 journalled through the spool shaft 15 to the baseframe 3 is disposed in the retractor 1 so that the webbing W is woundonto the spool 2. The retracting operation of the spool 2 is achieved bythe first reduction gear mechanism 10A and the second reduction gearmechanism 10B as two trains of different reduction gear ratios fortransmitting the rotational torque of the motor 5, the switching means70 for switching between the two trains according to a signal from thecontrol unit 9, the resistant torque means 60 disposed to effect one ofthe trains through the first reduction gear mechanism 10A and the secondreduction gear mechanism 10B according to the magnitude of therotational torque to be transmitted, the webbing withdrawal detectingunit 40 for detecting the activation of the motor or the rotation of thespool 2 due to the withdrawal of the webbing W, and the spool rotationdetecting unit 50. The control unit 9 is disposed to a portion of thevehicle to output an operational signal to the motor 5 of the retractor1. Connected to the control unit 9 through inputs I/F (not shown) arethe webbing withdrawal detecting unit 40, the spool rotation detectingunit 50, a buckle switch 8 built in a buckle 7 to inform that a tongueconnected to the webbing engages the buckle, and a plurality of externalsignal sensors S1 . . . Sn for informing various states of the vehicleduring running of the vehicle. Therefore, various signals indicatingvarious states of the occupant with the seat belt and various signalsindicating various running states of the vehicle are inputted into thecontrol unit 9. Based on the input signals, the control unit 9 controlsON/OFF of power sources for the CPU and the motor, and/or generatesoperational signals, such as control signals for the rotation of themotor and switching signals for switching the speed-reduction mechanism,to control the operation of the motor by the operational signals.

Description will now be made as regard to the structures of the webbingwithdrawal detecting unit 40 and the spool rotation detecting unit 50with reference to FIG. 8. For explaining the detecting units, FIG. 8schematically shows two sides of the seat belt retractor 1 where therespective detecting units are attached, in a state that the two sidesare arranged side by side.

As shown in the left half of FIG. 8, the webbing withdrawal detectingunit 40 comprises a switch plate 41 of a fan shape, a pivot pin 42 forjournalling the switch plate 41 as a hinge, a contact arm 43 extendingfrom the pivot pin 42 for a short length, and a limit switch 44 to beturned ON/OFF by the pivotal movement of the contact arm 43. The switchplate 41 is provided with guides 41 a on both ends thereof to limit thepivotal range (angle) of the switch plate 41. Within this range, an arcperipheral edge 41 b contacts a ring-like portion 21 of the spooldriving gear 20. The switch plate 41 is provided with an arc groove 41 cinside and along the arc peripheral edge 41 b, so that the peripheraledge 41 b is slightly deformed so as to apply pressure when theperipheral edge 41 b is in contact with the ring-like portion 21.Therefore, the switch plate 41 can pivot according to the rotation ofthe ring-like portion 21 without slippage. In FIG. 8, the switch plate41 (shown by two-dot chain lines) pivots in the counter clockwisedirection according to the rotation of the spool 2 in the clockwisedirection (corresponding to the withdrawal of the webbing W), with theresult that the limit switch 44 is turned ON.

Description will now be made as regard to the operation while the limitswitch 44 of the webbing withdrawal detecting unit 40 is turned ON. Inthe normal state, in case that the motor is activated by the operationof the CPU just like this retractor, the ON operation of an ignition keyof the vehicle may be a trigger for the power source Pw for the CPU.However, it is most effective that the power source Pw is turn ON by theoperation of withdrawal of the webbing. This also allows to make theapparatus compact. The time for tuning ON the power source Pw for theCPU when the webbing is withdrawn is detected by the webbing withdrawaldetecting unit 40.

The spool rotation detecting unit 50 is disposed outside the reellocking mechanism 4. The spool rotation detecting unit 50 detects therotational direction of the spool 2, i.e. the direction of withdrawingor winding of the webbing W, and a stopping state of the spool 2. Asshown in FIG. 1 and FIG. 8, the spool rotation detecting unit 50comprises a gear 51 attached on an end of the spool shaft 15 whichrotates coaxially with the spool 2, a train composed of three gears 52for reducing the rotational speed given through the gear 51, and avariable resistor 53 for detecting a value of resistance indicating thefinal rotational angle of the gear 51 obtained after the speedreduction. The rotational state of the spool 2 can be detected bydetecting the variation in voltage obtained through the variableresistor 53.

The actual operation of the webbing withdrawal detecting unit 40 will bebriefly explained. When the occupant stops the winding of the webbing Wor withdraws the webbing W while the webbing W is being wound by theoperation of the motor 5, the switch plate 41 pivots slightly so as toturn ON the limit switch 44. Therefore, the motor is stopped, so thatthe occupant can lightly withdraw the webbing W from the retractor 1. Asthe withdrawal of the webbing W is detected by at least one of thewebbing withdrawal detecting unit 40 and the spool rotation detectingunit 50, the motor is stopped. When the withdrawal of the webbing W isstopped, the motor 5 is turned ON to restart the winding of the webbingW.

As mentioned above, both the webbing withdrawal detecting unit 40 andthe spool rotation detecting unit 50 detect the rotation of the spool 2,and the detection functions as the trigger for the circuit. As shown inFIG. 8, for example, the power source Pw for the CPU may be turned ON byan OR circuit for the detecting units.

With regard to the pawl mechanism 70 to be engaged with the ratchetteeth 36 formed on the outer periphery of the internal gear 34 of theplanetary gear unit 30, two representative structural examples will beexplained and variations will be also explained briefly.

The structure and operation of the pawl mechanism 70 according to afirst structural example will now be described with reference to FIG. 2and FIGS. 9(a) through 9(c). The pawl mechanism 70 comprises a solenoid71 held by the inner surface of the casing 11 and a pivotal leverstopper 75. As shown in FIG. 9(a), the solenoid 71 has a plunger 72which slides within the coil thereof by excitation of the solenoid 71.The plunger 72 is retracted in the coil when the solenoid 71 is in theenergized state (excited state) and is pulled to its original state by aspring 73 when the excitation of the solenoid 71 is cancelled.

The lever stopper 75 journalled by a pivot shaft is disposed adjacent tothe plunger 72. The lever stopper 75 comprises a disk portion 75 acoaxial with the pivot, a driving lever 76 and a driven lever 77, whichare formed integrally with the disk portion 75 a to have a predeterminedangle therebetween about the pivot shaft. As illustrated, in theoriginal state, the driving lever 76 is biased by the spring 73 to havea position such that an end 76 a of the driving lever 76 extends to theend of the plunger 72. Disposed adjacent to the driven lever 77 is apawl 78 which can rotate about a pin formed on the disk portion 75. Inthe original state, the pawl 78 is held to be pushed against the drivenlever 77 by a wire spring 79 fitted around the disk portion 75. The pawl78 is provided with a releasing projection 78 a formed at the endthereof.

With reference to FIGS. 9(b) and 9(c), description will now be made asregard to the operation of the pawl mechanism 70 for engaging the pawlwith the ratchet teeth 36 of the internal gear 34 and for cancelling theengagement.

There are various modes for winding the webbing W. These modes include amode in which the webbing W is rapidly wound up with a large torque. Theoperation of rapidly winding up the webbing W is achieved bytransmitting the rotational torque of the motor 5 through the secondreduction gear mechanism 10B to the spool 2 by the reduced rotation ofthe carrier 33 for the planetary gears 32. Therefore, as mentionedabove, it is required to engage the pawl of the pawl mechanism 70 withthe ratchet teeth 36 formed on the outer periphery of the internal gear34 so as to lock the rotation of the internal gear 34.

FIG. 9(b) shows the state that the solenoid 71 is excited so that theplunger 72 is retracted in the coil of the solenoid 71. With theretraction of the plunger 72, the driving lever 76 of the lever stopper75 is pushed by the end 72 a of the plunger 72 to pivot in the counterclockwise direction. Accordingly, a portion of the pawl 78 projectingfrom the disk portion 75 a and arranged integrally with the driven lever77 is engaged with one valley of the ratchet teeth 36, thereby lockingthe rotation of the internal gear 34 in the clockwise direction. As aresult of this, the planetary gears 32 engaging the internal teeth 37 ofthe internal gear 34 revolves in the clockwise direction with a selfrotation in the counter clockwise direction. The revolution of theplanetary gears 32 makes the carrier 33 to rotate the spool 2 about thespool shaft 15 at a large reduction gear ratio.

The operation of the lever stopper 75 for cancelling the locking of theinternal gear 34 will now be described.

As the excitation of the solenoid 71 is cancelled from the state thatthe rotation of the internal gear 34 is locked, the plunger 72 extendsto project from the coil so that the driving lever 76 of the leverstopper 75 pivots in the clockwise direction. At the same time, thedriven lever 77 also pivots. Since the pawl 78 is in contact with one ofthe ratchet teeth 36 with a predetermined pressure at this point, theengagement between the pawl 78 and one of the ratchet teeth 36 is stillheld even when the driven lever 77 pivots. As the disk portion 75 afurther rotates, the pawl 78 pivots toward the driven lever 77 to passover the top of one tooth of the ratchet teeth 36 about the root of theprojection 78 a as its support by means of the return force of the wirespring 79. Therefore, the engagement between the pawl 78 and the ratchetteeth 36 is cancelled.

The structure and operation of a pawl mechanism 170 according to asecond structural example will now be described with reference to FIG.10 and FIGS. 11(a) through 11(d). As shown in FIG. 10 and FIG. 11(a),the pawl mechanism 170 comprises a solenoid 171 held by the innersurface of a retainer plate 120, a lever 175 which operates according tothe expansion of a plunger 172 of the solenoid 171, a first pawl 180 tobe engaged at its tip with one of the ratchet teeth 36 by the operationof the lever 175, and a second pawl 182 to be engaged at its tip withone of the ratchet teeth 36 according to the pivotal movement of thefirst pawl 180.

The solenoid 171 has the plunger 172 which slides within the coil whenthe solenoid 171 is excited. The plunger 172 is retracted in the coilwhen the solenoid 171 is in the energized state (excited state) and isextended to its original state by a releasing spring 190 and theoperation of the second pawl when the excitation of the solenoid 171 iscancelled.

The lever 175 journalled by a pivot shaft 184 is disposed adjacent tothe tip of the plunger 172. The lever 175 comprises a support 175 acoaxial with the pivot shaft 184, a driving lever 176 and a driven lever177, which are formed integrally with the support 175 a to have apredetermined angle therebetween. As illustrated, the driving lever 176has a forked tip 176 a engaging a small-diameter portion 172 a of theplunger 172, so that the driving lever 176 pivots according to thereciprocation of the plunger 172, with the result that the lever 175turns entirely about the pivot shaft 184.

The first pawl 180 is positioned below the driven lever 177 in such amanner that the first pawl 180 is movable along an elongated hole 186 bya biasing force of the releasing spring 190. The first pawl 180 issubstantially formed in an arc shape and is biased in a direction of anarrow A along the elongated hole 186 by the releasing spring 190connected to the rear end of the first pawl 180. The first pawl 180 isprovided with a notch into which a half at the top of the second pawl182 journalled by a pivot shaft 188 enters.

With reference to FIGS. 11(b) through 11(d), description will now bemade as regard to the operation of the pawl mechanism 170 for engagingthe pawl with the ratchet teeth 36 of the internal gear 34 and forcancelling the engagement.

As in the first structural example, the description will be made byreference to a case that the webbing W is rapidly wound up with a largetorque. As described above, the operation of rapidly winding up thewebbing W is achieved by transmitting the rotational torque of the motor5 through the second reduction gear mechanism 10B to the spool 2 by thereduced rotation of the carrier 33 for the planetary gears 32.Therefore, as mentioned above, it is required to engage the pawl of thepawl mechanism 170 with the ratchet teeth 36 formed on the outerperiphery of the internal gear 34 so as to lock the rotation of theinternal gear 34.

FIG. 11(b) shows the state that the solenoid 171 is excited so that theplunger 172 is retracted in the coil of the solenoid 171. With theretraction of the plunger 172, the driving lever 176 of the lever 175 ispulled by the end 172 a of the plunger 172 to pivot in the counterclockwise direction. Accordingly, the driven lever 177 also pivots aboutthe support 175 a. At this point, the driven lever 177 moves the firstpawl 180 positioned below the driven lever 177 to pivot in the counterclockwise direction against the biasing force of the releasing spring190, thereby engaging a projection 180 a formed on the bottom of thefirst pawl 180 with one valley of the ratchet teeth 36.

As shown in FIG. 11(c), as the internal gear 34 rotates about the shaft15 (the spool shaft) in the clockwise direction, the first pawl 180moves along the elongated hole 186 about the shaft 15 in the clockwisedirection in such a manner as to compress the releasing spring 190.Since the upper surface of the first pawl 180 is pressed and restrictedby the driven lever 177, the first pawl 180 is prevented from beingreleased. At this point, a portion of the notch 180 b of the first pawl180 presses the end 182 a of the second pawl 182 so as to move thesecond pawl 182 to pivot about the pivot shaft 188 in the counterclockwise direction, thereby locking the rotation of the internal gear34 in the clockwise direction. As a result of this, the planetary gears32 engaging the internal teeth 37 of the internal gear 34 revolves inthe clockwise direction with a self rotation in the counter clockwisedirection. The revolution of the planetary gears 32 rotates the spool 2about the spool shaft 15 at a large reduction gear ratio.

With reference to FIG. 11(d), the operation of the lever 175, the firstpawl 180, and the second pawl 182 for cancelling the locking of theinternal gear 34 will now be described.

As the excitation of the solenoid 171 is cancelled from the state thatthe rotation of the internal gear 34 is locked, the force for holdingthe plunger 172 within the coil is cancelled, so that the driven lever177 pivots about the pivot shaft 184 in the clockwise direction becauseof the biasing force of the releasing spring 190 in its extendeddirection (direction of arrow A). As a result of this, the force forrestricting and engaging the first pawl 180 with one of the ratchetteeth 36 is cancelled, so that the first pawl 180 pivots about the shaft15 in the counter clockwise direction to bring an end 180 c into contactwith a projection 182 b of the second pawl 182, thereby moving thesecond pawl 182 to pivot about the pivot shaft 188 in the clockwisedirection. In this way, the engagement among the ratchet teeth 36 of theinternal gear 34 and the two pawls 180, 182 can be completely cancelled.

According to the second structural example described above, it is notrequired to rotate the motor in reverse even for cancelling the locking.The engagement between the two pawls and the ratchet teeth can be easilycancelled by the two pawls, which is made by means of the biasing forceof the releasing spring.

Hereinafter, variations of the pawl mechanism 70 according to the firststructural example will be described in brief.

FIG. 12(a) shows an example in which the driven lever 77 is directlyengaged with the ratchet teeth 36. The pawl mechanism 70 of this exampleis provided with a roller R disposed on an end of the driven lever 77.The rotation of the roller R reduces friction between one of the ratchetteeth 36 and the end of the lever 77 so as to facilitate releasing ofthe end of the lever 77 from the ratchet teeth 36 when the plunger 72extends, and the driving lever 76 and the driven lever 77 rotatetogether in the clockwise direction.

FIG. 12(b) shows an example comprising a geared motor 91 and an arm-likestopper 92 disposed on the output shaft of the geared motor 91 in whichthe stopper 92 (pawl) is moved to pivot by the operation of the gearedmotor 91. FIG. 12(c) shows an example comprising a rack and pinionmechanism 90 in which a rack 90 a is brought into contact with theratchet teeth 36 by using a geared motor 91. In cases of FIG. 12(b) andFIG. 12(c), releasing of the stopper (pawl or rack) can be surelyachieved because of using the geared motor.

With reference to FIG. 13(a) through FIG. 15, description will now bemade as regard to the paths for transmitting the rotational forcethrough the first reduction gear mechanism 10A and the second reductiongear mechanism 10B achieved by the aforementioned mechanisms and to theoperation of the slip mechanism.

The rotational speed of the DC motor 5 of this embodiment is controlledby an open loop method according to pulse signals outputted from adriving circuit. In this embodiment, the control circuit is designed toallow the webbing to be wound with a small, middle, or large rotationaltorque by duty rates of three stages (25%, 50%, 100%). The relationbetween the actual using condition and the setting mode for winding thewebbing will be described later.

First, description will now be made as regard to the operation of therespective elements for the transmission of the rotation of the motor 5to the spool shaft 15 through the first reduction gear mechanism 10A forwinding the webbing with a small torque.

As shown in FIG. 13(a), as the motor 5 rotates at a low rotational speedin the counter clockwise direction for the purpose of winding up thewebbing, the reduction gear 13 rotates at a low rotational speed via thegear 12. Since the rotational torque of the reduction gear 13 at thispoint is lower than the preset torque for the rotor shaft 18 of therotary damper 17 disposed in the recess 13 a, the spool driving gear 20does not rotate relative to the reduction gear 13 and thus rotatestogether with the reduction gear 13. Therefore, the rotational torque ofthe reduction gear 13 is applied as the rotational force for winding upthe spool 2 without increase and decrease. According to the rotation ofthe spool 2, the carrier 33 of the planetary gear unit 30 integrallyattached to the spool 2, the sun gear 31 and the internal gear 34loosely fitted over the projection 15 a of the spool shaft 15 do notrotate relative to each other, but rotate integrally with the spool 2 inthe counter clockwise direction (see FIG. 14(a)).

Now, description will be made as regard to the operation of therespective elements for the transmission of the rotation of the motor 5to the spool shaft 15 through the second reduction gear mechanism 10Bfor rapidly winding the webbing W with large torque.

As shown in FIG. 13(b), as the motor 5 rotates at a high rotationalspeed in the counter clockwise direction for the purpose of winding upthe webbing, the reduction gear 13 rotates via the gear 12 at apredetermined reduction gear ratio. The sun gear 31 of the planetarygear unit 30 shown in FIG. 14 (b) rotates to make the same revolution asthe reduction gear 13. Since the pawl of the pawl mechanism 70 isengaged with the ratchet teeth 36 formed on the outer periphery of theinternal gear 34, the rotation of the internal gear 34 is locked.Therefore, the planetary gears 32 revolve with engaging the internalteeth 37 of the locked internal gear 34 according to the self rotationof the sun gear 31, and the carrier 33 journalling the planetary gear 32thus rotates in the counter clockwise directions. According to therotation of the carrier 33, a large rotational torque is transmitted tothe large-diameter portion of the spool shaft 15 through the socket 35.

Since the rotational torque of the reduction gear 13 at this pointexceeds the preset torque of the rotor shaft 18 of the rotary damper 17provided as the slip mechanism 60, the gear 19 of the rotary damper 17engaging the spool driving gear 20 rotates for braking with viscosityresistance. Thus, since the input from the reduction gear 13 is shut offby the slip mechanism 60, the rotation of the first reduction gearmechanism 10A is slipped, thereby preventing the train through the firstreduction gear mechanism 10A and the train through the second reductiongear mechanism 10B from being connected directly (FIG. 13(b)).

Furthermore, description will now be made as regard to a typicalcondition for activating the slip mechanism 60 with reference to FIG.15. As the occupant clasps the webbing W to stop the winding or towithdraw the webbing W while the motor 5 rotates at a low rotationalspeed, the spool driving gear 20 stops or rotates in the clockwisedirection. At this point, the motor 5 rotates in the counter clockwisedirection. As the rotation of the reduction gear 13 in the counterclockwise direction is stopped, the load is applied in reverse. At thispoint, the spool driving gear 20 with torque exceeding the preset torqueof the rotor shaft 18 of the rotary damper 17 rotates in a directionopposite to the rotational direction of the motor, thus causing slippageto the gear 19 of the rotor shaft 18. Since the withdrawal of thewebbing W is detected by the webbing withdrawal detecting unit 40, theoperation of the motor 5 is stopped, thereby allowing the occupant toeasily withdraw the webbing W.

Modes in which the motor is driven according to the control method ofthe seat belt retractor structured as mentioned above will be describedwith reference to flow charts shown in FIG. 16 through FIG. 18 anddiagrams showing changes of state when the webbing is wound shown inFIG. 19 and FIG. 20.

FIG. 16 is a flow chart showing the operational flow for controlling thewinding of the webbing. FIG. 17 is a flow chart showing the processingflow for setting the modes. FIG. 18 is a flow chart showing theoperational flow for improving the comfortableness for the occupantwearing the seat belt.

As described above, the speed of the DC motor 5 used in the seat beltretractor 1 can be set in detail by setting a voltage or setting pulsesignals in the control circuit. Therefore, the operational mode forwinding the webbing can be suitably set to correspond to movement of theoccupant wearing the seat belt and various external signals receivedduring movement of the vehicle, thereby achieving the minute windingoperation of the seat belt.

The operations in each mode corresponding to the state signal from apoint when the occupant wears the seat belt after getting on the vehicleto a point when the occupant takes off the seat belt for getting off thevehicle, and to the external signal obtained during running of thevehicle will be described in connection with the setting of therotational speed of the motor.

At the same time that the occupant sits on a vehicle seat, the occupantnormally pulls out the seat belt and inserts the tongue into the buckleat a side of the seat opposite to the side where the retractor ispositioned. At this point, the withdrawal of the webbing W is detectedby the webbing withdrawal detecting unit 40 of the retractor 1 so as toturn ON the power source Pw for the circuit and CPU (Step 100, Step110). The power source Pw may be turned ON according to an externalsignal by the activation of the ignition key or the like. By the statesignal indicating the detection of the webbing withdrawal, the operationof the motor 5 is stopped so as to cancel the winding of the webbing(Step 120, Step 130). After that, when the tongue is correctly engagedwith the buckle and thus the buckle switch 8 (see FIG. 7) built in thebuckle 7 is turned ON, the motor 5 rotates at a middle speed for windingup the webbing W in order to remove the excess amount of the seat beltto fit the seat belt to the occupant. This allows the webbing W toextend on the chest to the waist of the occupant without overpressure.As a result of this, slack of the webbing can be eliminated, so that theseat belt can be lightly fitted to the occupant's body (Step 150).According to a state signal indicating that the fitting of the webbingis achieved, the torque of the motor may be reduced or the operation ofthe motor may be stopped to eliminate the feeling of pressure to theoccupant. When the occupant moves largely forward from the statementioned above, the webbing is withdrawn according to this movement.After a point when the withdrawal of the webbing is stopped, the windingof the webbing is restarted in the same manner.

When a state signal indicating that the withdrawal of the webbing W isstopped in a middle thereof is inputted, the webbing W is wound up at apredetermined torque to be housed in the retractor 1 (Step 125, Step145).

As the occupant bends forward when the tongue is engaged with thebuckle, the webbing is further withdrawn. At this point, the operationof the motor 5 is stopped. When the occupant stops bending and returns,a state signal indicating that the withdrawal of the webbing is stoppedis inputted. According to the state signal, the motor is activated torestart the winding of the webbing. After the webbing is lightly fitted,the driving torque of the motor may be reduced or the operation of themotor may be stopped.

When the occupant is about to get off the vehicle, the webbing W isrequired to be wound up slowly after the tongue is disengaged and to bestored into the retractor within a pillar or the like for apredetermined amount. After that, when it is determined that thewithdrawal is not performed for a predetermined period, the power sourcePw for CPU is turned OFF by the circuit (Step 170 through Step 195).

In this manner, the comfortableness when the occupant puts on the seatbelt is improved. To further improve the comfortableness when theoccupant wears the seat belt, it is preferable to control the retractorto perform movements as described below. The description will be madewith reference to FIG. 18 and FIG. 20.

Conventionally, when the occupant slides the seat backward by means of aseat sliding mechanism or the like after wearing the seat belt, thewithdrawal of the seat belt is not detected. To cope with such asituation, the winding of the seat belt is repeatedly performed atpredetermined intervals, thereby cancelling the looseness of the seatbelt when wearing. Concretely, as shown in FIG. 18, when the withdrawalof the seat belt is detected, the predetermined winding is performed(Step 300, Step 310). When a predetermined time period passes after thewinding is completed (Step 320, Step 330), the winding is started again(Step 310) and whether the winding is enough is detected from thewebbing state (S340). When the winding is enough, the winding iscompleted (Step 350). This detecting loop is repeatedly performed atpredetermined intervals. In this way, the looseness of the webbing canbe completely cancelled while the occupant wears the seat belt.

In the present invention, the webbing can be wound by the motor forfitting the webbing to the occupant. At this point, the pressure on thechest of the occupant can be softened by controlling the speed of themotor. Concretely, the motor is set to have various speeds as shown inFIG. 20. The speed of the motor may be controlled by a known method,such as controlling PWM driving or controlling operational voltage. Thespeed control can be performed at predetermined intervals (for example,1 minute). In this speed control, the driving of the motor is stopped toreduce the tension on the seat belt for the purpose of facilitating thewithdrawal of the seat belt before the tongue is engaged with the buckleas shown in the variation diagram of FIG. 20. On the other hand, sinceit is preferable to quickly wind up the webbing immediately after thetongue is engaged with the buckle, the rise in speed of the motor atthis point is set to be the same as a conventional one.

During running of the vehicle, the motor is controlled mainly accordingto pulse signals corresponding to detected external signals. The motorcan be set in one of the following modes according to the state ofemergency.

Warning Mode

The main object of this mode is to inform an emergent situation to thedriver, for example, when a distance detecting sensor detects that thedistance from another vehicle in front of or behind the own vehicle isshorter than the preset value. The preset value for the distance fromanother vehicle can be variously set, for example, according to thevehicle speed. For example, when there is an object within apredetermined distance, the webbing is wound in order to inform thepresence of the object and the approaching state to the driver. Itshould be considered that the motor may be prevented from being set inthe warning mode when the vehicle is brought closer to an objectintentionally by the driver, such as for moving the vehicle into agarage, by using a speed of the vehicle, a relative speed to the object,a rate of change, and the like as factors.

Holding Mode

The object of this mode is to hold the occupant's body by winding up thewebbing, for a more emergent situation than that of the warning mode.For example, when the driver dozes during driving so that the driverbents forward while withdrawing the seat belt and a conventional dozedetecting sensor detects the doze of the driver, the winding of thewebbing by the motor in this mode functions as an alarm forstraightening the driver's posture and waking up the driver. When thevehicle runs on a bad road, a signal for activating the motor in thismode may be outputted to improve the safety by holding the driver and/oroccupant to the seat. In this case, as a trigger for outputting anexternal signal for this mode, an ABS operational signal and signalsfrom a steering angle sensor and a road surface sensor may be employed.

Pretensioning Mode

Conventionally, a seat belt device is equipped with a pretensioner forwinding up a predetermined amount of webbing when a vehicle collision oremergency deceleration is detected, thereby improving the effect ofrestraint of an occupant. When it is determined by a distance detectingsensor, such as a laser radar, that it is impossible to escape from avehicle collision, the webbing is rapidly wound up by the motor prior tothe collision. The speed of winding up the webbing should be set not toharm the occupant due to the rapid winding to prevent the secondaryaccident.

In Case of Fixing a Child Seat

A child seat is normally fixed to a seat by means of a webbing. As for aconventional child seat, it is required to withdraw the entire length ofthe webbing to fix the child seat to the vehicle seat for preventinglooseness during running of a vehicle. Accordingly, it is desired toprovide a dedicated mode to fix the child seat to the vehicle seat. Forexample, a child seat switch is provided. When the switch is turned ON,the webbing is tightly wound until the child seat is fixed to thevehicle seat with a relatively large torque.

FIG. 17 is a flow chart showing processes for the respective modes. As asignal of setting one of the modes is inputted to the control circuitfrom an external sensor or the like during running of the vehicle orwhile the child seat is fixed, the speed and/or the time period forwinding up the webbing is set corresponding to the mode (Step 310, Step320, Step 330). For switching the speed-reduction mechanism 10, thetrain change is started (solenoid of the pawl mechanism 70 is excited),so that the rotational torque of the motor is transmitted to the spool 2through the second reduction gear mechanism 10B (Step 340). The windingof the webbing W is performed in the mode (Step 350). In case a signalfor cancelling the aforementioned mode or a signal indicating that thesafety is ensured is inputted, the train change is finished (Step 370).

As the child seat switch is turned ON for mounting the child seat, thetrain change is started to wind up the webbing W for a predeterminedperiod (Step 400 to Step 420). In case of taking off the child seat, thebuckle switch is turned OFF when the tongue is disengaged from thebuckle (Step 430). The train change is finished (Step 370) when it isdetected that the buckle switch is turned OFF, so that the mode isreturned to the comfort mode of slowly winding the webbing.

In the hold mode or in the warning mode, the speed of the motor ispreferably set to provide a medium rotational torque. In thepretensioning mode, the speed of the motor is preferably set to providea large rotational torque.

FIG. 19 is a variation diagram indicating conditions for winding thewebbing, schematically showing the relation among the signal current fordriving the motor for winding the webbing, the withdrawing amount of thewebbing, and the tension for winding up the webbing into the retractor,which are measured to be fed back to the control circuit. The abscissaof this diagram indicates elapsed time (t) which is scaled for roughlyshowing the elapsed time relative to the movement of the occupant and tothe state of the vehicle. Among the curves in the diagram, a signalcurrent curve indicates the state of driving of the motor, a withdrawingamount curve indicates the movement of the webbing withdrawn from theretractor, and a tension curve indicates a pulling force by the occupantand a winding force by the operation of the motor. As apparent from thediagram, the operation of the motor is controlled according to the stateof the webbing withdrawn from the retractor, thereby suitablycontrolling the tension of the webbing.

Hereinafter, variations of the entire structure and the respectivecomponents of the speed-reduction mechanism 10 will be described.

FIG. 21(a) through FIG. 21(e) are schematic explanatory views showingvariations of the entire structure of the speed-reduction mechanism 10.

In FIG. 21(a), the first reduction gear mechanism 10A and the secondreduction gear mechanism 10B are separately disposed and thetransmission of the rotational torque of the motor 5 is allowed to beswitched by shifting the switch gear 70. The shift of the switch gear 70is achieved by sliding its shaft or moving the switch gear 70 along theshaft. In this case, since the slip mechanism 60 does not effect thesecond reduction gear mechanism 10B, a large rotational torque can beeffectively outputted. The switching between the train through the slipmechanism 60 and the train through the second gear mechanism 10B fortransmitting the rotational torque of the motor 5 may be performed bythe operation of a solenoid 71 as shown in FIG. 21(b) instead of theswitch gear. FIG. 21(c) shows a variation in which the switch gear 70 isdisposed between the second reduction gear mechanism 10B and the slipmechanism 60. As shown in FIG. 21(d), the switching of the train for themotor may be performed directly between the first reduction gearmechanism 10A and the second reduction gear mechanism 10B and theconnection between the spool 2 and the slip mechanism 60 can beestablished or cut by the solenoid 71.

FIG. 21(e) shows a variation of the speed-reduction mechanism comprisinga single train in which the rotational torque of the motor 5 istransmitted to the spool 2 through the first reduction gear mechanism10A and the slip mechanism 60. Because in this mechanism, weight isgiven to the operation ability in the comfort mode, it is preferablethat the operation of winding up the webbing with a large torque in theevent of emergency is performed by other biasing means.

FIGS. 22(a) through 22(c) are schematic explanatory views showingvariations of the first reduction gear mechanism 10A. On the basis ofits function for securely transmitting the rotational torque from theshaft of the motor to the output shaft 25, such as a shaft for windingup the webbing, a pulley 6P is disposed to oppose the shaft of the motorto transmit the torque of the motor to the output shaft 25 of thespeed-reduction mechanism through a transmitting belt 22 (see FIG.22(a)).

Employed as the transmitting belt 22 include a timing belt, belts havingvarious section (V, plane), a resin wire, a steel wire, a chain and thelike.

As a speed-reduction mechanism, a planetary gear unit 23 may beemployed. In this case, a planetary gear side (carrier 23 a) forsupporting the planetary gears or internal teeth of an internal gear 23b is an input shaft, so that the torque from the input shaft can betransmitted to the output shaft 25 (see FIGS. 22(b), 22(c)).

The mechanism for switching from the train through the first reductiongear mechanism to the train through the second reduction gear mechanismto obtain large torque will be described. FIG. 23(a) shows a variationin which the carrier of the planetary gear unit 23 is locked so as tooutput the input from the sun gear to the output shaft through theinternal teeth of the internal gear 23 b. FIGS. 23(b) and 23(c) show avariation in which the transmission from the input 24 to the output 25coaxially arranged is achieved by an intermediate gear 26. Theintermediate gear 26 can be shifted by a clutching operation. The inputshaft 24 and the output shaft 25 may be arranged to have different axesto compose a gear train through the intermediate gear 26.

FIGS. 24(a) and 24(b) show examples of a magnetic-particle clutch inwhich magnetic particles 95 are filled in a space between the internalgear 34 and a flange 93, which has substantially the same diameter asthe internal gear 34 and is disposed adjacent to the internal gear 34,and an electromagnetic coil 94 is guided by the flange 93 to be woundtherearound. In this magnetic-particle clutch, the coil 94 is excited tomake the magnetic particles in the solid state, thereby locking therotation of the internal gear 34. FIG. 24(a) shows an example in whichthe magnetic-particle clutch is arranged along a side surface of theinternal gear 34, and FIG. 24(b) shows an example in which themagnetic-particle clutch is arranged along the outer periphery of theinternal gear 34.

Now, a variation of the slip mechanism 60 will be described. Though theslip mechanism 60 using the rotary damper 17 is employed in thisembodiment, variations using a frictional mechanism or a spring biasingmechanism as a torque limiter may also be employed. FIG. 25(a) shows aslip mechanism 60 in which disks are prevented from rotating with atorque less than a predetermined torque by a plate spring 63. The platespring 63 is attached to a flange of an inner disk 61 and is providedwith a brake pad 64 attached to its end. The brake pad 64 presses aflange 62 a of an outer disk 62 so as to apply slide resistance.Therefore, the inner and outer disks 61, 62 rotate together until thetorque of the outer disk 62 exceeds a predetermined value. FIG. 25(b)shows a variation in which a ring-like vane 66 is provided on the outerperiphery of the inner disk 61. The outer disk 62 has a ring-like oilchamber 65 in which silicone oil is sealed, and the ring-like vane 66 isarranged coaxially with the outer disk 62. In this case, also, the innerand outer disks 61, 62 rotate together until the viscosity resistancedeveloped by the vane and oil around it exceeds a predetermined value.

As shown in FIG. 25(c), a slip mechanism 60 may be arranged and formedas an outer ring, and a spiral spring 67 is arranged to be compressedwithin an inner space of the slip mechanism 60. With this structure, arotational torque by the biasing force of the spiral spring 67 istransmitted to an outer ring 62 until exceeding a predetermined torque.After exceeding the predetermined torque, the slip mechanism 60 shutsoff the rotational torque developed by the biasing force. As shown inFIG. 25(d), instead of the spiral spring 67, a compressed spring coil 67may be employed to exhibit its biasing force according to apredetermined rotational angle.

FIGS. 26(a) through 26(d) show examples of a slip mechanism 60 disposedbetween an outer disk 62 and an inner bush 61 arranged coaxially withthe outer disk 62. In the slip mechanism 60 shown in FIG. 26(a), theouter disk 62 is provided with a transfer curve 62 b corresponding to ¼circle and a step portion 62 a on the inner periphery thereof, and asteel ball 68 is housed at the terminal end of the transfer curve 62 b.The inner bush 61 is provided with a radially extending notch in which aspring S is placed. By the spring S, the steel ball 68 is held at theterminal end of the transfer curve 62 b. In the slip mechanism 60, thesteel ball 68 does not pass over the step portion 62 a so that the innerbush 61 and the outer disk 62 rotate together when the torque is smallerthan a preset value. As the rotational torque exceeding the preset valueis applied, the steel ball 68 passes over the step portion 62 a, travelsfor a full circle along the inner periphery of the outer disk 62 withbeing pressed by the spring S and enters in the position at the terminalend again.

FIG. 26(b) shows a variation in which a spring S as a torque limiter iscompressed between a small-diameter inner bush 61 and an outer disk 62.As shown in this figure, the outer end of the spring S is inserted intoa recess 62 d formed in the inner periphery of the outer disk 62 anddoes not come off the recess 62 d with bending of the spring caused bytorque less than a preset torque. Therefore, the inner bush 61 and theouter disk 62 rotate together. As the rotational torque applied exceedsa preset value, the outer end of the spring S slides along the innerperiphery of the outer disk 62. After the terminal end slides for a fullcircle, the terminal end enters into the recess 62 d again.

FIG. 26(c) shows a slip mechanism 60 similar to that shown FIG. 26(a).In this slip mechanism 60, an elastic ball 69 is employed. The elasticball 69 is deformed in the radial direction and pressed against theinner periphery of the outer disk 62 by pressure of the spring S. As arotational torque exceeding the preset value is developed between theinner bush 61 and the outer disk 62, the elastic ball 69 isshear-deformed to cancel the engagement between the inner bush 61 andthe outer disk 62, so that the inner bush 61 and the outer disk 62separately rotate.

FIG. 26(d) shows a variation of the slip mechanism shown in FIG. 25(a).The flange of the outer disk 62 is clamped between two inner bushes 61 aand 61 b, wherein the distance between them can be controlled by screws61 c so as to obtain desired resistant torque. If necessary, springs(not shown) may be attached to the screws 61 c for controlling thepressure on the disk of the inner bush 61.

Variations of the webbing withdrawal detecting unit 40 will be describednow. Instead of the fan-like switch plate 41 (see FIG. 8), variations ofa switch detecting the webbing withdrawal are shown in FIGS. 27(a) and27(b).

FIG. 27(a) shows a withdrawal detecting unit 40 comprising a ring 46provided with a trigger projection 46 a formed on the periphery thereofand a bush 45 which can rotate relative to the ring 46 with apredetermined resistance. The bush 45 directly rotates by the rotationof the spool (not shown). When the rotational torque is less than theresistance, the ring 46 rotates together with the bush 45. A limitswitch 44 is turned ON by the trigger projection 46 a. FIG. 27(b) showsa withdrawal detecting unit for turning ON the limit switch 44 in whicha ring-like spring 47 functioning as a cramping ring is fitted onto thebush 45, and the limit switch 44 is turned on by the integral rotationof the bush 45 and the spring 47 with the aid of friction between thebush 45 and the biasing force of the spring 47. Instead of theknown-type limit switch used in this embodiment, a normal contact switchmay be used. Further, a photodetector may be used. In this case, a slitis formed in a switch plate or a ring and the switch plate or the ringrotates so that the photodetector receives light passing through theslit. Alternatively, a proximity sensor of sensing metal which candetect the movement of a metallic switch plate or a metal ring or a Hallelement which can detect change in magnetic field may be used.

The spool rotation detecting unit will be described hereinafter. In thespool rotation detecting unit, instead of the aforementioned variableresistor for directly detecting change in voltage, a photodetector ofencoder type, a photodetector for detecting the position of the slitwhich can used also for the withdrawal detecting unit, a proximitysensor, or a magnetic detector for reading a position by a magnetic headmay be used.

Though the DC (direct current) motor is used as a motor in thisembodiment, various known servo motors which are variable speed motorsmay be used. For example, a stepping motor, an ultrasonic motor, an ACmotor may be used with a corresponding motor driving circuit, therebyachieving the winding operation as mentioned above. It is preferable bythe reason of wiring harness that the control circuit for driving themotor is positioned in a space below the webbing winding-up portioncreated when the motor is assembled in such a manner that the controlcircuit is disposed adjacent to the motor. However, the motor may bepositioned in any suitable place in a frame.

As described above, the present invention can provide seat belt windingfunctions suitable for various conditions of the occupant. Thesefunctions are set at standard values in shipping from a factory. Anoccupant can simulate these modes (simulating function) so as to changethe effects of the functions to prefer degrees. This operation can beperformed by using a display of a navigation system installed in thevehicle or using an exclusive controller.

In addition to a function of providing alarm sounds and messages in thewarning mode and the pretensioning mode, a function of providing varioussounds or displaying operation confirmation images may also be added inthe comfort mode, thereby improving the operation ability.

These settings may be made via harnesses arranged in the vehicle so thata driver's seat is set separately from other seats or all of the seatsare set to the same. These settings for the respective seats may be madethrough telecommunication lines. For example, the setting mode of theretractors for the respective seats can be set corresponding to commandswhich are inputted by the driver or another occupant with theaforementioned display or a remote controller via telecommunicationlines using any known protocols. Data used for these settings mayinclude IDS for specifying the seats and commands for setting therespective modes (warning, holding, pause (waiting), releasing, childseat fixing).

As described above, a retractor of this invention can provide suitablestates of winding up a webbing corresponding to various conditions bycontrolling the state of a single motor having a speed-reductionmechanism with high adaptability or by combination of such a motor witha known retractor, thereby securely providing comfort and safety for anoccupant.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

What is claimed is:
 1. A control method of a seat belt retractorcomprising: applying a webbing of a seat belt to an occupant andfastening a tongue to a buckle, automatically winding the webbingseveral times repeatedly with a predetermined interval therebetween forpreventing looseness of the webbing on the occupant, determining whethera further winding of the webbing is needed to prevent the looseness ofthe webbing after a predetermined time from a last winding of thewebbing, and if necessary, winding the webbing again, receiving at leastone of signals selected from a state signal showing a movement of theoccupant wearing the seat belt and an external signal obtained fromdetecting means installed in a vehicle during running thereof,controlling a rotation of a spool for the webbing by switching arotational torque of a motor to a predetermined reduction ratiocorresponding to at least one of the state signal and the externalsignal, or controlling a driving state of the motor to a predeterminedtorque, to thereby wind the webbing on the spool, winding the webbingwhen the tongue is disengaged from the buckle, and turning OFF a powersource of a control circuit for operating the motor upon detection of asituation that winding of the webbing is accomplished or that thewebbing has not been withdrawn for a predetermined period of time.
 2. Acontrol method of a seat belt retractor as claimed in claim 1, whereinthe state signal includes a signal showing withdrawal of the webbingwhile the webbing is in a winding state, a rotation of the motor beingstopped based on the state signal.
 3. A control method of a seat beltretractor as claimed in claim 1, wherein the state signal includes asignal showing that the tongue of the webbing is engaged with the buckleof the webbing, by which the motor is driven with such torque as to windthe webbing to fit the webbing onto the occupant.
 4. A control method ofa seat belt retractor as claimed in claim 3, wherein the state signalincludes a signal showing that fitting of the webbing is accomplished,by which the torque of the motor is reduced or driving of the motor isstopped.
 5. A control method of a seat belt retractor as claimed inclaim 1, wherein the state signal includes a signal showing thatwithdrawal of the webbing is canceled, by which the motor is started torestart a winding of the webbing.
 6. A control method of a seat beltretractor as claimed in claim 1, wherein in a condition that the tongueof the seat belt is engaged with the buckle of the seat belt, when thewebbing is withdrawn and stopped, winding of the webbing is started at atime of interruption of the withdrawal of the webbing, and after fittingthe webbing to the occupant, the torque of the motor is reduced ordriving of the motor is stopped.
 7. A control method of a seat beltretractor as claimed in claim 6, wherein the torque of the motor forfitting the webbing to the occupant is set lower than a torque of themotor for winding of the webbing made just after the tongue is engagedwith the buckle.
 8. A control method of a seat belt retractor as claimedin claim 1, wherein the state signal includes a signal showing that thetongue of the webbing is disengaged from the buckle of the webbing, andby disengagement of the tongue from the buckle, the motor is activatedto wind the webbing into the retractor.
 9. A control method of a seatbelt retractor as claimed in claim 1, wherein at a same time of or aftera predetermined period of time from detection of withdrawal of thewebbing, a power source of a control circuit for operating the motor isturned ON.
 10. A control method of a seat belt retractor as claimed inclaim 1, wherein a speed of the motor is controlled to change a speed ofwinding of the webbing by the motor.